Fine Minerals

Minerals are the substances that make up the rocks of the Earth’s crust. Scientists have identified over 3,000 minerals. Most of these are rare and look insignificant.

Just around twenty common minerals make up most of the Earth’s crust.

Occasionally some minerals form crystals large enough to be seen. These crystals occur in many different shapes and colours and they can form beautiful and attractive objects.

author : Kenneth James

Citrine crystal group

Tungsten Mining

Tungsten is a heavy, grey metal with a very high melting point giving it many roles in technology, including its use as the filament in electric light bulbs.

The town of Pasto Bueno, in Ancash Department, Peru is the centre of tungsten mining. The metal is found in the quartz veins of an igneous rock mass, occurring as huebnerite (manganese tungstate).

Here and there in the veins, where there is a cavity, crystallisation has occurred, producing quartz and huebnerite crystal groups. The black huebnerite and transparent quartz crystals form striking sculptural pieces.

The museum purchased this Pasto Bueno huebnerite and quartz group in June 1977 for £150.00, from an Englishman Mr M.W.J. Townsend. It was one of a consignment of mineral samples that he had bought some months earlier from street traders in the Peruvian mining towns.

Gold in Rare Crystal Shape

Gold has been treasured as a precious metal since earliest times. Its attraction is its rich yellow metallic lustre, resistance to rust, and softness which allows it to be easily worked by goldsmiths.

The geology of the formation and occurrence of gold is complicated and the exploration for gold deposits is a specialist task.

Gold usually occurs as shapeless flakes and nuggets. However, occasionally gold forms crystals.

This fragment of conglomerate rock contains an octahedral crystal of gold. This is a rare occurrence and this gold specimen is worth more in its crystal shape than melted down for bullion. The Ulster Museum bought this gold sample from Sotheby’s, London, in 1968. The only information known about it was that it was from Brazil.

In 1976 a gold prospector, Mr James Stewart called into the museum to examine this specimen. He declared that it came from the Oro Preto goldfield in Brazil. This is the oldest goldfield in Brazil. Its name comes from the Portuguese for ‘black gold’, because the first gold nuggets found there were stained black with iron oxide.

Rare Minerals

Over 3,000 minerals are known to scientists. Most of them are rare and are found sparingly at only a few places in the world. In fact, most of the Earth’s crust is made up of just eight chemical elements, which combine together to form twenty common rock-forming minerals. Many of the minerals on show in the museum’s Earth’s Treasures display are rare, seldom encountered by geologists in the course of their work.

Wulfenite is lead molybdate; mimetite is lead arsenate. The thin wulfenite plates are fragile and crystal groups such as this have to be handled carefully.

This piece was bought from the Mineral gallery, London in 1975 for £136.00.

Eye Agate

Agate is a microcrystalline variety of silica (silicon dioxide), characterised by fineness of grain and colour banding. It is found in volcanic rocks worldwide. It is a hard mineral and it has been used in jewellery since earliest times.

There are many colour and pattern varieties of agate and there is a bewildering array of names used to describe them. When some agates are cut, the angle and position of the cutting slices through internal banding, exposing these structures as ‘eyes’.

Canon John Grainger (1830-91) was Church of Ireland Rector of Broughshane, County Antrim. He assembled a huge collection of 60,000 natural history and archaeological objects in his rectory. In 1891, shortly before his death, he donated it to Belfast Corporation. It was one of the founding collections of the Ulster Museum.

This piece of polished Eye Agate is from the ‘Grainger Collection’. Canon Grainger affixed this verse from Holy Scripture (Zechariah, Chapter 9, verse 9) to the back of the specimen: "For behold the stone that I laid before Joshua; upon one stone shall be seven eyes."

Fool's Gold

Pyrite is the most abundant sulphide mineral in rocks of all ages. It is found in all three of the major rock types — igneous, sedimentary and metamorphic.

Pyrite is iron sulphide and it is commonly found with other ore minerals, such as galena and sphalerite.

The brassy colour and metallic sheen of pyrite leads to it being mistaken for gold, giving rise to its popular name ‘Fool’s Gold’. Real gold can be identified by its softness and heavy weight.

Pyrite can form beautiful clusters of crystals in a variety of shapes. In recent times Peru has produced some of the finest pyrite specimens in the world. They came from mines in the Peruvian mountains and were sold from markets set up in the centre of Lima. The high quality of the pyrites attracted international dealers and soon Peruvian pyrite became available world-wide.

The museum bought this specimen in 1975 for £175.00 from an English traveller Mr M.W.J. Townsend, who had bought the piece in Peru.

Rose Quartz

Quartz is the crystalline variety of silica (silicon dioxide). It is the second most abundant mineral in the Earth’s crust, after feldspar. It occurs worldwide in many rock types and in many environments.

There are different varieties of quartz based upon colour:

Rock Crystal (clear, flawless)

Citrine (yellow/brown)

Amethyst; (purple)

Smoky Quartz (black)

Milky Quartz (white)

Rose Quartz (pink).

Rose Quartz is the least common of the quartz colour varieties. It rarely forms crystals occurring mainly as shapeless veins in rock. It is not much used in jewellery, because of its cloudy appearance. However, it is a popular collector’s item because of its attractive rose tints. Some women believe that it can improve the skin, heal women’s complaints and cure broken hearts.

This Rose Quartz crystal group is from Governador Valadares, Minas Gerais, Brazil. The city is the centre of a rich gem-producing area, exporting gem minerals and finished gemstones around the world. This piece was bought from the Hatton Garden dealers ‘Roughgems’ in 1978 for £125.00.

Gemstones and Minerals

A gemstone is a naturally occurring mineral that has been artificially polished, faceted and shaped for decorative purposes. The mineral must be hard enough to withstand wear and tear. The most sought after gemstones are clear, attractively coloured and free from flaws.

A semi-precious stone that displays a dazzling and surpassing variety of colours is tourmaline. It has red, pink, violet, blue, green, brown, black and colourless varieties. Some crystals display two or three colour bands along their length in shades of green and red.

The red tourmalines are called ‘Rubellite’, from the Latin rubellus meaning ‘reddish’

This specimen is from the Julius Hanna Collection of minerals. It was bought by the museum from his widow in 1926 for £50.00. Nothing is known about Mr Hanna, except that he was gentleman of means, who lived in Strandtown, in east Belfast.

Crystal Sprays

Gypsum, which is calcium sulphate, is a common mineral found at many localities around the world. It is a soft mineral, far too soft to be used in jewellery. It is however, sought after by mineral collectors, because it can form beautiful crystals, in varied and sometimes fantastic shapes.

In Victoria, Australia, a gypsum vein produces arrangements of bladed crystals topped by sprays of needle-shaped crystals, forming a vision of a mineral flower bed.

This specimen, which is very fragile, required special packing for its safe carriage. It was bought from mineral dealer Max Davis of Oxford Street, London in 1975 for £120.00.

Width 400mm

Accession number: I 2738

Gypsum crystal arrangement (close-up view), from Victoria, Australia.

New Blue Mineral

Cavansite is one of the world’s rarest minerals. Until some years ago it was known from only one place: Lake Owyhee State Park, in Oregon, U.S.A., where it was discovered in 1967 as small blue specks in the local rock.

The mineral’s name ‘cavansite’ comes from its chemical composition: calcium vanadium silicate.

In recent years large cavansite specimens have been discovered in the Whagoli basalt quarry, in Poona, India. They occur as sprays of blue crystals set amongst pale-coloured zeolite minerals. Whagoli cavansite has become popular with mineral collectors. The museum bought this piece from an American dealer in 2009 for £979.